Influence of drugs acting on nitric oxide-dependent pathways on ethanol tolerance in rats

Tolerance to alcohol: A critical yet understudied factor in alcohol addiction

Alcohol tolerance refers to a lower effect of alcohol with repeated exposure. Although alcohol tolerance has been historically included in diagnostic manuals as one of the key criteria for a diagnosis of alcohol use disorder (AUD), understanding its neurobiological mechanisms has been neglected in preclinical studies. In this mini-review, we provide a theoretical framework for alcohol tolerance. We then briefly describe chronic tolerance, followed by a longer discussion of behavioral and neurobiological aspects that underlie rapid tolerance in rodent models. Glutamate/nitric oxide, γ-aminobutyric acid, opioids, serotonin, dopamine, adenosine, cannabinoids, norepinephrine, vasopressin, neuropeptide Y, neurosteroids, and protein kinase C all modulate rapid tolerance. Most studies have evaluated the ability of pharmacological manipulations to block the development of rapid tolerance, but only a few studies have assessed their ability to reverse already established tolerance. Notably, only a few studies analyzed sex differences. Neglected areas of study include the incorporation of a key element of tolerance that involves opponent process-like neuroadaptations. Compared with alcohol drinking models, models of rapid tolerance are relatively shorter in duration and are temporally defined, which make them suitable for combining with a wide range of classic and modern research tools, such as pharmacology, optogenetics, calcium imaging, in vivo electrophysiology, and DREADDs, for in-depth studies of tolerance. We conclude that studies of the neurobiology of alcohol tolerance should be revisited with modern conceptualizations of addiction and modern neurobiological tools. This may contribute to our understanding of AUD and uncover potential targets that can attenuate hazardous alcohol drinking.

Selective mu- and kappa-opioid receptor antagonists administered into the nucleus accumbens interfere with rapid tolerance to ethanol in rats

BACKGROUND

Previous findings have shown that intra-accumbens injection of naltrexone, a non-selective opioid antagonist, blocks the acquisition of rapid tolerance to ethanol in rats. This study investigates the effects of intra-accumbens injection of the selective mu-, delta-, and kappa-opioid antagonists, respectively, naloxonazine, naltrindole, and nor-binaltorphimine, on rapid tolerance to ethanol.

METHODS

Male Wistar rats with guide cannulae directed to the shell or the core portions of the nucleus accumbens received a microinjection of naloxonazine (2-4 microg), naltrindole (2-4 microg), nor-binaltorphimine (2.5-5 microg), or vehicle. After 5 min, each group was divided in two groups that received ethanol (2.7 g/kg i.p.) or saline. Rats were then tested for motor coordination on the tilting plane apparatus. Twenty four hours later, all rats received a challenge dose of ethanol (2.7 g/kg i.p.) and were tested on the tilt plane again.

RESULTS

Repeated injections of ethanol caused a reduction in motor impairment suggesting the development of tolerance. However, rats injected with 4 microg naloxonazine into either core or shell portions of the nucleus accumbens did not exhibit tolerance when challenged with ethanol on day 2. Rats treated with 5 microg nor-binaltorphimine into accumbens core plus intraperitoneal saline on day 1 showed reduced motor impairment when challenged with ethanol on day 2, suggesting cross-tolerance to ethanol.

CONCLUSIONS

Taken together, our results suggests that mu-opioid receptors in both shell and core portions of the nucleus accumbens, and possibly kappa-opioid in the core, participate in the modulation of rapid tolerance to ethanol.

Effects of SR141716 and WIN 55,212-2 on tolerance to ethanol in rats using the acute and rapid procedures

RATIONALE

Our previous findings have shown rapid cross-tolerance between ethanol and Delta(9)-tetrahydrocannabinol and that intraperitoneal (i.p.) injection of cannabinoid receptor type 1 (CB1R) antagonist SR141716 (SR) does not interfere with tolerance to either of these drugs in mice.

OBJECTIVES

This study investigates the effects of SR, alone or in combination with the CB receptor agonist WIN 55,212-2 (WIN), on the development of acute and rapid tolerance to the incoordinating effect of ethanol in rats.

MATERIALS AND METHODS

Male Wistar rats received SR, through i.p. (0.5-2.0 mg/kg) or intracerebroventricular (i.c.v.) injections (0.5-4.0 microg), alone or together with WIN (1.0 microg, i.c.v.), in combination with ethanol (2.7 g/kg, i.p.). Another group received WIN (1.0 microg, i.c.v.) in combination with ethanol (2.3 g/kg), and the rats were tested for motor coordination. Rapid tolerance was assessed 24 h later by administering ethanol to all animals and retesting them under the same dose regimen. Acute tolerance was evaluated for 75 min after ethanol (3.0 g/kg, i.p.) in animals treated with SR or WIN (i.c.v.).

RESULTS

The reduced motor impairment on day 2 (i.e., rapid tolerance) was blocked by SR (i.p. and i.c.v.). WIN (1.0 microg, i.c.v.) facilitated rapid tolerance and also prevented the blockade of rapid tolerance by SR (1.0 microg, i.c.v.). In the acute tolerance procedure, SR did not affect the motor incoordination induced by ethanol.

CONCLUSIONS

The results suggest that the endocannabinoid system may contribute to the development of rapid tolerance to ethanol.

Behavioral Cross-Tolerance between Repeated Intracerebellar Nicotine and Acute Δ9-Tetrahydrocannabinol-Induced Cerebellar Ataxia: Role of Cerebellar Nitric Oxide

We have previously demonstrated that acute intracerebellar nicotine or N-methyl-4-(3-pyridinyl)-3-buten-1-amine (RJR-2403), a selective alpha(4)beta(2) nicotinic acetylcholine receptor (nAChR) agonist, dose dependently attenuates Delta(9)-tetrahydrocannabinol (Delta(9)THC)-induced ataxia. Presently, we have shown that intracerebellar nicotine (1.25, 2.5, and 5 ng; once daily for 5 days) and RJR-2403 (250, 500, and 750 ng; once daily for 5 days) significantly attenuate cerebellar Delta(9)-THC-induced ataxia dose dependently, suggesting the development of cross-tolerance between nicotine or RJR-2403 with Delta(9)-THC in male CD-1 mice. Intracerebellar RJR-2403 (750 ng) microinfused for 1, 2, 3, 5, and 7 days (once daily) significantly attenuated Delta(9)-THC-induced ataxia in the 3-, 5-, and 7-day treatment groups; optimal cross-tolerance was evident at day 5 and persisted till 36 h after the last RJR-2403 microinfusion. Intracerebellar microinfusion of hexamethonium (nAChR antagonist; 1 microg) or dihydro-beta-erythroidine hydrobromide (alpha(4)beta(2) nAChR antagonist; 500 ng) for 5 days 10 min before daily intracerebellar nicotine or RJR-2403 microinfusion virtually abolished cross-tolerance between nicotine or RJR-2403 and Delta(9)-THC, indicating nAChR participation. In addition, microinfusion of antagonists 10 min after daily intracerebellar nicotine or RJR-2403 failed to alter the cross-tolerance, suggesting possible involvement of downstream cerebellar second-messenger mechanisms. Finally, the cerebellar concentration of nitric oxide products [total sum of nitrite + nitrate (NO(x))] was increased after 5 days of intracerebellar nicotine or RJR-2403 treatment, which was decreased by acute intracerebellar Delta(9)-THC treatment. The "nicotine or RJR-2403 + Delta(9)-THC" treatments significantly increased cerebellar NO(x) levels compared with treatment with Delta(9)-THC alone, supporting a functional correlation between cerebellar nitric oxide production and cerebellar Delta(9)-THC-induced ataxia and suggesting participation of nitric oxide in the observed cross-tolerance between nicotine/RJR-2403 and Delta(9)-THC.

Effect of isopregnanolone on rapid tolerance to the anxiolytic effect of ethanol

OBJETIVE: It has been shown that neurosteroids can either block or stimulate the development of chronic and rapid tolerance to the incoordination and hypothermia caused by ethanol consumption. The aim of the present study was to investigate the influence of isopregnanolone on the development of rapid tolerance to the anxiolytic effect of ethanol in mice. METHOD: Male Swiss mice were pretreated with isopregnanolone (0.05, 0.10 or 0.20 mg/kg) 30 min before administration of ethanol (1.5 g/kg). Twenty-four hours later, all animals we tested using the plus-maze apparatus. The first experiment defined the doses of ethanol that did or did not induce rapid tolerance to the anxiolytic effect of ethanol. In the second, the influence of pretreatment of mice with isopregnanolone (0.05, 0.10 or 0.20 mg/kg) on rapid tolerance to ethanol (1.5 g/kg) was studied. CONCLUSIONS: The results show that pretreatment with isopregnanolone interfered with the development of rapid tolerance to the anxiolytic effect of ethanol.

Possible role of mouse cerebellar nitric oxide in the behavioral interaction between chronic intracerebellar nicotine and acute ethanol administration: Observation of cross-tolerance

Many studies have reported cross-tolerance between nicotine and ethanol. Previously we demonstrated that intracerebellar nicotine attenuates ethanol-induced motor impairment. In this study, intracerebellar nicotine (0.625, 2.5, 5 ng; once daily for five days) significantly attenuated ethanol-induced motor impairment in a dose-dependent fashion suggesting the development of cross-tolerance between nicotine and ethanol in male CD-1 mice. Using the same paradigm, intracerebellar nicotine (5 ng) microinfused for 1, 2, 3, 5, 7 days significantly attenuated ethanol-induced motor impairment in all groups except the 1-day treatment group. Cross-tolerance, which developed optimally in 5-day nicotine treatment group, was reversible and detectable up to 40 h post-nicotine microinfusion. Intracerebellar microinfusion of hexamethonium (1 mug once daily for 5 days): (i) did not alter ethanol-induced motor impairment indicating no tonic nicotine receptor involvement; (ii) 10 min prior to daily intracerebellar nicotine treatment virtually abolished the cross-tolerance between nicotine and ethanol indicating nicotinic acetylcholine receptor participation; (iii) when microinfused 10 min after daily intracerebellar nicotine treatment, failed to abolish the cross-tolerance which suggested possible participation of downstream second messenger mechanisms. Chronic intracerebellar microinfusion of nicotine: (i) failed to attenuate acute pentobarbital (25mg/kg i.p.)-induced motor impairment; and (ii) produced no change in normal motor coordination when followed by saline injection. Finally, the cerebellar concentration of total nitric oxide products (nitrite+nitrate; NO(x)); (i) was increased after 5-day intracerebellar nicotine; (ii) was decreased by acute ethanol administration; and (iii) decreased due to acute ethanol administration which was opposed by chronic intracerebellar nicotine treatment. These results support a functional correlation between the cerebellar nitric oxide production and ethanol-induced motor impairment and suggest possible participation of nitric oxide as a factor in the observed cross-tolerance between nicotine and ethanol.

Antagonism of ethanol ataxia by intracerebellar nicotine: possible modulation by mouse cerebellar nitric oxide and cGMP

We have reported previously that intracerebellar nicotine attenuates ethanol ataxia via nicotinic-cholinergic receptors. We report now that attenuation of ethanol ataxia by intracerebellar nicotine is modulated by cerebellar nitric oxide-guanylyl cyclase (GC) messenger system. Intracerebellar microinfusion of SNP (sodium nitroprusside, a nitric oxide donor; 15, 30, and 60 pg) and SMT (S-methylisothiourea; 70, 140, and 280 fg; an inhibitor of inducible nitric oxide synthase), significantly enhanced and reduced, respectively, intracerebellar nicotine-induced attenuation of ethanol ataxia in a dose-related manner. Similarly, intracerebellar isoliquiritigenin (an activator of GC; 1, 2, and 4 pg) and ODQ (1H [1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one, an inhibitor of GC; 375, 750, and 1500 fg), significantly enhanced and reduced, respectively, intracerebellar nicotine-induced attenuation of ethanol ataxia in a dose-related fashion. These results suggest that the functional interaction between nicotine and ethanol may involve modulation by cerebellar nitric oxide and cGMP. Intracerebellar microinfusion of isoliquiritigenin (4, 8, and 16 pg) in the absence of nicotine significantly attenuated ethanol ataxia dose-dependently indicating a tonic involvement of cGMP in ethanol ataxia. Finally, intracerebellar nicotine (5 ng) significantly increased and ethanol 2 g/kg i.p. decreased levels of total cerebellar nitrite+nitrate (NOx) which were functionally correlated with ethanol ataxia and its attenuation by intracerebellar nicotine. The ethanol-induced decrease in NOx was significantly antagonized by intracerebellar nicotine. The NOx data further supported an involvement of nitric oxide in the behavioral interaction between nicotine and ethanol. Overall, the results of the present investigation demonstrate a functional correlation between cerebellar nitric oxide messenger system and the behavioral interaction between nicotine and ethanol.

The effects of intracerebroventricular application of 8-Br-cGMP and LY-83,583, a guanylyl cyclase inhibitor, on sleep-wake activity in rats

Cyclic GMP is the second messenger that mediates most of the neuronal effects of nitric oxide (NO). Several lines of evidence suggest that NO-ergic mechanisms play an integral role in the regulation of vigilance. In the present study, we tested the effects of the activation of cGMP-receptive mechanisms and the inhibitor of guanylyl cyclase (GC), LY-83,583, on sleep in rats. Rats were injected intracerebroventricularly (icv) with 0.16, 4, 100, and 500 microg or 2.5 mg 8-Br-cGMP, a membrane-permeable analogue of cGMP, or 1 and 100 microg LY-83,583. Administration of 4 microg-2.5 mg 8-Br-cGMP increased wakefulness and suppressed rapid-eye-movement sleep (REMS) and non-REMS (NREMS) in rats when given before dark onset but not when given before the light period. The GC inhibitor LY-83,583 strongly promoted NREMS and suppressed REMS during the light period of the day. Furthermore, LY-83,583 induced striking increases in the delta-wave activity of the electroencephalogram (EEG) during NREMS, whereas EEG activity above the 4.5 Hz wave range was suppressed in all vigilance states. Our finding that cGMP has an arousal-promoting activity is in line with the hypothesis that NO/cGMP signaling pathway is involved in the regulation of vigilance.

Systemic and intra-accumbens microinjections of naltrexone interfere with tolerance to ethanol in rats

RATIONALE

Evidence suggests a role for the opioid system in the control of ethanol reinforcement and drinking. Previous findings have shown that naltrexone, an opioid antagonist that decreases ethanol consumption in humans and experimental animals, reduces the acquisition of acute ethanol tolerance in rats. However, there are few data regarding the role of the opioid system in the acquisition of ethanol tolerance, particularly in brain areas involved in the rewarding actions of ethanol.

OBJECTIVES

This study investigates the effects of systemic and of intra-accumbens injections of naltrexone on the development of rapid tolerance to ethanol.

METHODS

Wistar rats received intraperitoneal injections of naltrexone (0.1-3.0 mg/kg) or microinjections into the core or shell portions of the nucleus accumbens (5-20 microg) before ethanol (2.7 g/kg i.p.). The animals were tested for motor coordination on the tilting plane apparatus. Tolerance was assessed 24 h later by administering the same dose of ethanol to all animals and retesting them on the tilting plane.

RESULTS

The second injection of ethanol resulted in less motor incoordination on Day 2, suggesting the development of rapid tolerance. Pretreatment with naltrexone, either i.p. (0.3 and 0.6 mg/kg) or intra-accumbens (5-20 microg), on Day 1, blocked the development of rapid tolerance to the motor-incoordinating effects of ethanol on Day 2 without affecting the motor performance of the animals on Day 1.

CONCLUSIONS

The results suggest that the opioid system may be involved in the development of ethanol tolerance, and that the nucleus accumbens may play a role in this phenomenon.

Inhibition of nitric oxide release in vivo by ethanol

OBJECTIVE

Previous studies indicate that the nitric oxide (NO(.)) pathway is involved in the acute or chronic effects of ethanol on the central nervous system. However, direct evidence for the effect of ethanol on NO(.) production in vivo is lacking, and it is not clear whether it is inhibition or stimulation of the NO(.) pathway that contributes to the behavioral effects of ethanol. Herein the release of NO(.) in the rat striatum in vivo in response to NMDA receptor activation--the dominant mechanism controlling NO(.) formation-has been investigated after systemic or local injections of ethanol.

METHODS

NMDA-induced release of authentic NO(.) was measured directly in the striatum of urethane-anesthetized (1.2 g/kg intraperitoneally) male Sprague-Dawley rats by using a direct-current amperometric method coupled to an electrically modified carbon microelectrode. An injector cannula was implanted in the proximity of the electrode (250 microm apart) for focal drugs application.

RESULTS

Local application of NMDA (1 microl, 100 microM) produced a sharp and transient NO(.) signal. Systemic ethanol, 1 or 2.5 g/kg intraperitoneally, caused a long-lasting, dose-dependent inhibition of NMDA-induced NO(.) release to 12.2 +/- 5.9 and 6.4 +/- 3.7% of control, respectively, 60 min after ethanol administration. Dizocilpine (0.5 mg/kg intraperitoneally) mimicked the ethanol effect, inhibiting NO release to 1.6 +/- 0.66% of control. Local application of ethanol (1 microl, 2.5% v/v) in the striatum reduced the NMDA-induced response to 28.6 +/- 3.8% of control. Focal application of the competitive NMDA receptor antagonist D-(-)-2-amino-5-phosphonopentanoic acid (100 microM) or the nonselective NO synthase inhibitor L-N(G)-nitro-arginine methyl esther (100 microM) also caused inhibition of NMDA-induced NO(.) release to 2.4 +/- 0.7 and 4.3 +/- 0.9% of control, respectively.

CONCLUSIONS

Ethanol, at pharmacologically significant doses, strongly inhibits striatal NO(.) production and release apparently through inhibition of NMDA receptor function. Inhibition of NMDA receptor-mediated activation of the NO(.) pathway could be a primary neurobiological mechanism contributing to the effects of ethanol.

Involvement of nitric oxide-dependent pathways of dorsolateral periaqueductal gray in the effects of ethanol in rats submitted to the elevated plus-maze test

Our previous study showed the microinjection of drugs that influence the nitric oxide (NO)-mediated neurotransmission in the hippocampus impacts upon the anxiolytic-like effect of ethanol. In this study, we examined whether NO-dependent pathways of the dorsolateral periaqueductal gray (dlPAG) participate in the anxiolytic effect of ethanol in rats submitted to the elevated plus-maze test. We evaluated the impact on ethanol effects of the nitric oxide synthase (NOS) inhibitor 7-nitroindazole, the soluble guanylate cyclase inhibitor 1H-(1,2,4)-oxodiazolo (4,3-a) quinoxalin-1-one (ODQ), the cyclic guanylate monophosphate (cGMP) analogue 8-bromo-cGMP and the NO donor sodium nitroprusside. The results showed that ODQ and 7-nitroindazole increased the percentage of open arm entries and of time spent on open arms in the elevated plus maze in rats injected with ethanol at 1.0g/kg, a dose that did not produce anxiolysis per se. Conversely, 8-bromo-cGMP and sodium nitroprusside blocked the increased exploration of open arms exhibited by rats treated with a higher dose of ethanol (1.2g/kg). Taken together, the results suggest that the inhibition of NO-dependent pathways of the dlPAG enhances the anxiolytic effect of ethanol, whereas the activation of these pathways results in an opposite effect.